Again, the ball would have a tendency to curve in the direction of rotation were there no resistance from the air. For, in the plane of rotation the circumference at c moves more rapidly toward A than at the point b (Fig. 3); hence it has a tendency to advance over a greater distance than b in a given time, but is held back by b. This gives centrifugal and centripetal forces acting from b to c, and a consequent tendency of c to revolve around b, which, in connection with the motion of both toward a, would give the curved line a-A′ as the path of the ball. [Illustration: FIG. 3.] As a familiar example, take a child’s wooden hoop and toss it from you with sufficient upward tendency to overcome gravity, at the same time causing it to revolve rapidly in a plane parallel to the horizon, and you will find that it will describe a curve in the direction of the rotation and fall at your feet. This is an extreme illustration of this factor of the base-ball curve; the diameter of the hoop being so much the greater, of course gives a far greater velocity of rotation in comparison to that of projection than the smaller diameter of the base-ball can give. This same principle is involved in the explanation of the motion of the boomerang of the Australians and the toy of the same name. Yours sincerely, ROBERT S. DOD. * * * * * Our thanks are due to the young friends whose names here follow, for pleasant letters which they have sent us, but which are crowded out of the “Letter-box”: Arthur E. Clark, Jr., A. G. C., M. M. Stevens, Urbanna Myrover, “Gladys, Gipsy, Sibyl,” Blue Bell, “Hie” and “Tie,” T. A. T., May Elden, Herman N. Steele, “Yum” and “Tum,” Daisy Smith, Phil Riley, Annie M. Porter, Daisy A. C., Lucy E. D., Mable H. W., Amelia N. F., and Annie L. D., Francie Mackenzie, “Maiden Hair and Moonlight,” Mabel F. Rigby, W., I. S. B., E. T. C., Carl W., Isabel Eldridge, Kittie Loper, Aimée and Goldina Mendelson, Herbert A. Megraw, Gerald B. Wadsworth, F. W. L., Amy D. Smith, Imogene Avis, May, David Blair, and May E. Masten. [Illustration: The Agassiz Association SIXTY-SIXTH REPORT.] LOUIS AGASSIZ. HIS LIFE AND CORRESPONDENCE.[2] No person capable of appreciating a beautiful record of a consistent and noble life can begin to read Mrs. Agassiz’s book and leave it unfinished; and no one can finish reading it without receiving a fresh baptism of faith, hope, and love.